The invention relates generally to watercraft, and more particularly to watercraft incorporating drag-reducing features.
Drag is a critical aspect of the design of watercraft. Designers are constantly striving to reduce drag not only to improve efficiency, but also to allow watercraft to reach greater speeds.
There are five major sources of drag acting on a watercraft: form drag, interference drag, skin friction, wave drag, and induced drag. Form drag results from the vehicle's shape as well as the cross-sectional area of the vehicle. Interference drag results from vortex shedding. Skin friction results from the friction of the water rubbing against the skin of the vehicle. Wave drag results from the energy carried away from the vehicle by waves as it moves through the water. Finally, induced drag results from redirecting the flow of fluid. This kind of drag results from items such wings as they generate lift.
A technique to reduce watercraft drag is to minimize the surface area of the watercraft in contact with the water. A boat employing a hydrofoil to lift its hull out of the water is one example of a watercraft employing this technique. Disadvantageously, however, the weight of the boat must be lifted out of the water, resulting in induced drag at the hydrofoil as it deflects water downward to provide the necessary lift.
A technique commonly used to achieve greater speed is called “planing.” To achieve planing, a boat typically has a broad, relatively flat hull toward its rear. As greater and greater power is applied, the front of the boat lifts and oncoming water is directed downward by the flat section of the hull. The boat gradually shifts from being supported mainly by buoyant forces to being mainly supported by hydrodynamic lift forces. Disadvantageously, however, planing is typically inefficient and requires a lot of power.
There exists a need for a way of reducing drag that would enable watercraft to achieve high efficiencies and greater speeds.